Ignoring HTML 3 tags can certainly destroy some dicument structure. For
example, ignoring IDs can break many hyperlinks of the #xxx variety. Also,
ignoring containters like NOTE can cause distinct blocks of text to run
together in undesired ways (hence the HR abuse now rampant in HTML 3
docs... my own included.) Having browsers treat the new containers like
<P> and recognize IDs would go a long way towards increasing the number of
people writing HTML 3.